Trepanning of cased explosives by etching



Oct. 29, 1963 H. J. PLUMLEY TREPANNING OF CASED EXPLOSIVES BY ETCHING \NVENTOR HAROLD J. PLUMLE Y United States Patent 3,103,918 TREPANNING GF AED EXPLUSiVES BY El Cl llNG Harold J. Plumlay, Washington, D6. Filed Jan. 12, that, Ser. No. 511%?) 7 Claims. (til. 156-18) (Granted under Title 35, US. Code (E52), see. 2%)

This invention relates to processes of, and apparatus for, forming an opening or openings in metallic casings and other enclosures, the invention being of particular utility in gaining access to the interiors of bombs, projectiles, and other items of explosive ordnance, especially where such items have been so constructed that the forming of openings therein is intrinsically difiicult. Many such items are so constructed as to present the greatest possible difliculty to any attempts at opening the same without detonating the explosive contents, anti-disturbance devices, and other means being provided to cause the bomb to explode, if mechanical operations are performed upon it, which cause noise or movement of the bomb.

It has heretofore been proposed to form an opening in such a cased explosive, in order to permit dearming and/or removal of the explosive contents through such opening, by means of a corrosive liquid circulated in contact with the casing for a sufiicient length of time to permit the liquid to eat its way through the case, and thus form an opening therein. One method so used in the past has involved the use of a container adapted to be clamped or otherwise held in position upon the top of the bomb, and constructed to function as a percolating device, a column of the corrosive liquid being supported with its lower end resting upon the case, the liquid in the column and associated container being circulated by the bubbles of gas formed in the reaction rising through the column of liquid. The percolating process, however, has met with only partial success, and accidents involving unwanted detonation have occurred for the reason that upon the formation of the first small opening in the top of the case, the entire body of fluid pours through the opening into the interior of the bomb. Since the liquid is at boiling temperature, and the hole formed is relatively small, this may result in throwing against the opening a quantity of molten explosive from within the case, in such manner that the explosive solidifies and reseals the opening. The temperature and pressure may then rise within the case to such a point as to cause detonation. An additional hazardous factor resides in the fact that the corrosive liquid may be of such nature as to form sensitive explosive compounds within the bomb.

In accordance with the present invention, the difficulties above outlined are circumvented by using a novel spray arrangement, in which a corrosive liquid is projected against the case, preferably the side or bottom, in such manner that the sprayed area, although relatively large, is one from which the corrosive liquid may run freely, most of the liquid thus remaining outside the bomb, even after the formation of the first opening or openings. The above outlined dangers due to accidental rescaling, and due to the entry of a relatively large quantity of boiling reagent into the interior of the case, are thus obviated.

T repanning of the case by the use of a corrosive spray, in the manner outlined, if it is to be successfully performed, requires the observation of a few critical factors, although if these factors are observed, the operation is simple, safe, and results in the formation of a large opening relatively quickly. Moreover, in practicing the present invention it is not necessary to disturb or touch the bomb in any manner whatever. Furthermore, dur- "ice 2 ing the actual trepanning operation, and for any desired time thereafter, all personnel may remain at a safe distance. it also requires only a very short time to set up the apparatus, which is extremely compact, portable, and easy to handle.

"It will be understood that the primary objects of the invention are the achievement of the very simplicity, safety, lightness and ease of handling above described. Additional objects and advantages will become apparent during the course of the following description, taken in conjunction with the drawings forming a part hereof.

In the drawings:

FEG'URE 1 is a perspective view of a projector or sprayhead constructed in accordance with the present invention, fragmentarily showing its supporting means, and also fragmentarily illustrating a bomb casing against which a spray from the head is being directed in the performance of a trepanning operation.

FIGURE 2 is a front elevational view of the spray head and a supporting clamp therefor.

FIGURE 3 is a cross-sectional view taken substantially on the line 3-3.0f FIGURE 2 and looking in the direction of the arrows. Referring now to the drawing; in the corrosive trepanning of steel, the most effective reagent thus far discovered is a 35 percent solution of nitric acid. Grade B technical nitric acid is entirely satisfactory and may be diluted with water to yield a solution having a gravity of 1.22 to 1.23 as measured by an ordinary battery hydrometer. This corresponds to acid of absolute percentage 35 to 37. In the absence of a hydrorneter, preparation may be efiected by mixing three parts of the technical acid (58 to 60 percent) with two par-ts of water. The best reagent thus far discovered for the trepanning of aluminum, is acidulated cupric chloride solution.

It is preferable that the reagent be projected uniformly against the case, over a fairly large case area, and that the projection be at a rate not exceeding. about 1.5 cubic centimeters per second. Slower projection speeds result in corrosion at less than the maximum rate. Faster rates of projection result in an extremely inefficient utilization of the reagent, and worse, a complete cessation of corrosive action is apt to occur due to the cooling of the surface by the liquid flow and the ensuing establishment of a passive layer on the metal.

Preferably only a gravity head is used, and the head may be as low as 38 inches, but should not be greater than 50 inches. No auxiliary air or steam supply is required. An air driven atomizer is also unnecessarily complex, and in fact is a positive disadvantage for the reason that passivity in the nitric acid reaction is encouraged by the evaporative cooling occasioned by the air steam.

The reagent is dispersed by causing two fine coplanar jets of liquid, each having a diameter of about .0225 inch, to intersect each other at a angle. This jet arrangement has been determined by considerable trial and experimentation to be quite critical. Two and only two jets are used, in the attainment of best performance, and their included angle must be between 85 and while it has also been found that performance suffers to a marked degree if the jet diameter varies materially from the range between .020 and .030 inch.

The construction of the projector or spray head is clearly shown in FIGURES 2 and 3. The threadedly interfi-tted sect-ions l and 2, which form its body are preferably polystyrene plastic. This material has been found to be substantially inert to the indicated reagents. A gasket 3, of inert synthetic rubber, such as Koroseal, may be interposed to prevent escape of the liquid reagent except through the jet orifices 5, which are formed in the member 2. As best indicated in FIGURE 3, the jet openings discharge convergently into a conical depression '7, axially formed in the dischar e end of the substantially cylinrical female member 2. The jet openings are coplanar, at 90 to one another, and each at approximately 45 to the longitudinal axis of the assembly. As previously indicated their diameter is preferably .0225 inch. Peripheral grooves 8 and 9, may be formed in members 1 and 2 respectively, to permit convenient supporting of the assembly by lashing if preferred, although as indicated in the drawings, the nozzle assembly may also be effectively supported by fitting a suitably apertured sheet metal supporting bracket between the threaded body sections 1 and 2, the bracket inturn being mounted, as by means of the bolt 12, upon the end of a suitably formed supporting arm as 14. The other end of the arm may simply be stuck into the ground or supported in any other convenient fashion. Wing nut 13 may be employed to permit convenient assembly, disassembly and adjustment of the positioning of the spray head.

A glass or other suitable container (not shown) for the reagent, having a bottom outlet or siphon outlet, may be supported in a convenient manner at a height of from 38 to 50 inches above the nozzle, and connected to the nozzle by a tube 15, of synthetic rubber or other inert material. Nozzle element 1 is provided with a nipple 4 for convenient attachment of the tube. The projector or spray head is preferably positioned about 8 inches from the case to be trepanncd. if it is more convenient to position the container at a greater elevation above the spray head than 50 inches (as with the bottle on the ground surface above a deep crater) the effective head, and hence the flow rate must be cut down by means of a stop cool; or pinch clamp restriction in the tube line.

In the case of the nitric acid-steel reaction, if the bomb case temperature is 60 F. or above, the corrosion will start about 15 seconds after the acid spray is stanted. In cold climates or in winter, the bomb case must be preheated locally to about 70 F. before the reaction will start. This is most easily done by applying a blowtorch flame to the desired spot until it feels slightly warm to the hand. This operation, although apparently hazardous, is entirely safe due to the great thermal inertia of a heavy metal case.

Once the gear is set up in the manner described, and the solution of the case by the spray jet is in progress, the operation requires no further attention. if considered desirable, all personnel may absent themselves from the vicinity until the operation is completed, which may be indicated, for instance, by an empty reagent bottle.

In view of the fact that black oxide scale, P6304, commonly found on castings and hot rolled steel, is completely insoluble in nitric acid, it must be removed, if present, before commencement of the trepanning open ation. Dry or hydrated Pe O ordinary iron rust, is similarly insoluble in nitric acid, so that this also must be removed if present. The best known reagent for the removal of both of these is hydrochloric acid. This may be ordinary laboratory concentrated acid diluted with an equal volume of water. About 300 cubic centimeters of this solution sprayed onto the scale or rust covered surface by the same projector or spray head will completely clear the desired area in from 3 to 4 minutes.

it will also be apparent that if the surface is painted, the paint must be removed before commencing the trepanning operation. If the bomb or other explosive device is suspected to contain an anti-disturbance element, paint remover may be used to remove the paint without disturbing the bomb. Of course, if it is quite certain that no such anti-disturbance device is present, paint, rust and/ or scale may be removed by filing or scraping rather than in the manner described.

,ice,

While it will be apparent that the preferred embodiment of my invention herein described is Well calculated to fulfill the objects and advantages primarily stated, it is to be understood that the invention is subject to variation, modification and change Within the spirit and the scope of the subjoined claims.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim: I

l. The method of gaining access to the interior of a metallic casing containing explosive material comprising directin a spray of liquid which is corrosive with respect to said casing against a selected section thereof from which liquid will run freely, regulating said spray to a rate not exceeding 1.5 cubic centimeters per second for a period long enough to form an opening therein whereby said section is dissolved at the optimum safe and economical speed.

2. The method of claim 1 in which the metallic casing comprises ferrous material and the liquid comprises an aqueous solution containing approximately 35 percent nitric acid.

3. The method of claim 1 in which the metallic casing comprises alu iinum and the liquid comprises acidulated cupric chloride solution.

4. The method of claim 1 in which the spray is formed by impinging coplanar jets of the liquid.

5. The method of claim 1 in which the spray is formed by two coplanar jets emitted from orifices having diameters of .020 to .030 inch, the jets impinging at an included angle of 35 to 105 degrees at a velocity corresponding to a head of said liquid behind the orifices of approximately 38 to 50 inches.

6. The method of gaining access to the interior of a metallic casing containing explosive material comprising selecting a section of the casing from which liquid will run freely, and directing against said section at a rate of approximately 1.5 cubic centimeters per second a spray of liquid which is corrosive with respect to the casing for a period long enough to form an opening through the section, said spray being formed by coplanar jets impinging at an angle of approximately after emission from two orifices of approximately .0225 inch diameter under a head of approximately from 38 to 50 inches of the liquid, whereby said section is dissolved at the optimum safe and economical speed.

7. The method of gaining access to the interior of a corroded metal casing containing explosive material comprising directing against a selected section of the casing from which liquid will run freely, at a rate not exceeding approximately 1.5 cubic centimeters per second, a spray initially of hydrochloric acid to remove products of corrosion from the metal casing and thereafter of a liquid which is corrosive with respect to the casing for a period long enough to form an opening therein, whereby said section is issolved at the optimum safe and economical speed.

References Cited in the file of this patent UNITED STATES PATENTS 247,151 Beggs Sept. 20, 1881 764,082 Thorpe July 5, 1904 964,126 Smith et al July 12, 1910 1,164,128 Sexton Dec. 14, 1915 2,166,990 Gray July 25, 1939 2,336,846 Clark Dec. 14, 1943 FOREIGN PATENTS 388,411 France of 1908 305,616 Germany Jan. 6, 1920 

1. THE METHOD OF GAINING ACCESS TO THE INTERIOR OF A METALLIC CASING CONTAINING EXPLOSIVE MATERIAL COMPRISING DIRECTING A SPRAY OF LIQUID WHICH IS CORROSIVE WITH RESPECT TO SAID CASING AGAINST A SELECTED SECTION THEREOF FROM WHICH LIQUID WILL RUN FREELY, REGULATING SAID SPRAY TO A RATE NOT EXCEEDING 1.5 CUBIC CENTIMETERS PER SECOND FOR A PERIOD LONG ENOUGH TO FORM AN OPENING THEREIN WHEREBY SAID SECTION IS DISSOLVED AT THE OPTIMUM SAFE AND ECONOMICAL SPEED. 